Field
A technology according to the disclosure relates to an image generating apparatus, an image generating method, and a storage medium.
Description of the Related Art
A tomographic image is an image of internal structures of a solid object (such as the human body or the earth) by observation and recording of differences in effects on passage of waves of energy impinging on those structures. Optical coherence tomography (OCT) is a noninvasive imaging test that uses light waves to take cross-section pictures of, for example, a retina, which is the light-sensitive tissue lining the back of an eye. As a method of obtaining a tomographic image of a measurement object such as a living matter in a nondestructive and noninvasive manner, an optical coherence tomography (hereinafter, will be referred to as OCT) has been put into practice. The OCT is widely used, particularly in an ophthalmic diagnosis relating to the eye and its diseases.
According to the OCT, a tomographic image of a measurement object is obtained while light reflected from the measurement object interferes with light reflected from a reference mirror, and an intensity of the interfering light is analyzed. Apparatuses that obtain the above-described optical coherence tomography have been proposed, including a time domain OCT apparatus configured to obtain depth information of the measurement object by changing a position of the reference mirror, a spectrum domain OCT (spectral domain optical coherence tomography: SD-OCT) apparatus configured to separate the interfering light and replace the depth information with frequency information to be obtained, and a wavelength-sweeping light coherence tomography (swept source optical coherence tomography: SS-OCT) apparatus configured to previously separate a wavelength to be output. It should be noted that the SD-OCT and the SS-OCT are also collectively called Fourier domain optical coherence tomography (FD-OCT).
Angiography, or arteriography, is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. In recent years, a blood vessel radiographic contrasting method using FD-OCT has been proposed, and this blood vessel radiographic contrasting method is called OCT angiography. U.S. Patent Application Publication No. 2014/0221827 discloses an OCT angiography in which a variation of a logarithmic intensity of an interfering signal is set as a motion contrast feature quantity, and imaging of the motion contrast feature quantity is performed.
According to the method disclosed in U.S. Patent Application Publication No. 2014/0221827, while a value that is 10 decibel (dB) above a noise floor average value is set as a threshold, this threshold is compared with an intensity of the interfering signal, and the motion contrast feature quantity corresponding to the intensity of the interfering signal below the threshold is set as 0.
However, a signal intensity of noise or a signal intensity of the blood vessel varies in accordance with a position or a layer in a depth direction of the retina in a tomographic image obtained by an actual OCT. For this reason, in a case where the threshold is set as a fixed value as in U.S. Patent Application Publication No. 2014/0221827, there are probabilities that the noise is regarded as the blood vessel and the blood vessel is regarded as the noise depending on the position or the layer in the depth direction of the retina. That is, there are probabilities that imaging of the blood vessel is not carried out at a high accuracy according to the related art technology.